Question 1

What is the difference between '==' and 'is'?

Accepted Answer

**Target Audience:** Beginners preparing for Python interviews — no prior Python knowledge assumed.
**Difficulty:** Easy
**Python version:** Behaviour checked on CPython 3.11 (python3.11 and the in-page Pyodide 0.25.1 runtime, which is CPython 3.11.3); the warning text was also checked on 3.12.

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact word an interviewer expects. Every output shown in the **Veri

Question 2

What are mutable and immutable types in Python?

Accepted Answer

**Target Audience:** Beginners preparing for Python interviews — no prior Python knowledge assumed.
**Difficulty:** Easy
**Python version:** Behaviour checked on CPython 3.11 (python3.11 and the in-page Pyodide 0.25.1 runtime, which is CPython 3.11.3).

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact word an interviewer expects. Every output shown in the **Verified** section was copied from a real run o

Question 3

How do you work with dictionaries (get, setdefault, items, merging)?

Accepted Answer

**Target Audience:** Beginners preparing for Python interviews — no prior knowledge assumed beyond variables and lists.
**Difficulty:** Easy
**Python version:** Checked on CPython 3.11 and the page runner (Pyodide 0.25.1 = CPython 3.11.3). The `|` and `|=` operators need Python 3.9 or newer.

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:` — the precise word an interviewer expects you to use. Every output shown was produced by act

Question 4

How does slicing with start:stop:step work?

Accepted Answer

**Target Audience:** Beginners preparing for Python interviews — you only need to know what a list and a string are.
**Difficulty:** Easy
**Python version:** Checked on CPython 3.11 and the page runner (Pyodide 0.25.1 = CPython 3.11.3); the bytecode comparison was also run on CPython 3.12.

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:` — the precise word an interviewer expects you to use. Every output shown was produced by actua

Question 5

What is the difference between append, extend and insert on a list?

Accepted Answer

**Target Audience:** Beginners preparing for Python interviews — you need to know what a list is; nothing more.
**Difficulty:** Easy
**Python version:** Checked on CPython 3.11 (64-bit Linux) and the page runner (Pyodide 0.25.1 = CPython 3.11.3, a 32-bit WebAssembly build).

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:` — the precise word an interviewer expects you to use. Every output shown was produced by actually running the

Question 6

How does iterable unpacking work?

Accepted Answer

**Target Audience:** Beginners to intermediate Python developers — you should know what a list and a tuple are.
**Difficulty:** Easy
**Python version:** Behaviour and `dis` output checked on CPython 3.11 (3.12 where noted); the examples also run in the page on Pyodide 0.25.1 (CPython 3.11.3).

> **How to read this doc:** Ideas come in plain language first. Words an interviewer expects you to use are tagged `📌 Interview term:` and defined on the spot, then listed again in the Quick Glossary. All

Question 7

How do you read TOML with tomllib in Python 3.11+?

Accepted Answer

**Target Audience:** Python developers who configure apps or tools, explained from zero
**Difficulty:** Easy
**Python version:** Behaviour checked on CPython 3.11, 3.12 and 3.13 (and in the page's Pyodide 3.11 runtime)

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words an interviewer expects. Every output block in the **Verified** section was copied from a real run of the examples on this page.

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Question 8

Is Python pass-by-value or pass-by-reference?

Accepted Answer

**Target Audience:** Beginners preparing for Python interviews — especially if you learned C, C++ or Java first and want to map the terms.
**Difficulty:** Easy
**Python version:** Behaviour checked on CPython 3.11.17 and in the page runner (Pyodide 0.25.1, CPython 3.11.3).

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words an interviewer expects. All output shown was produced by actually running th

Question 9

How do you read and write files in Python?

Accepted Answer

**Target Audience:** Beginners learning Python, and anyone who wants the precise answer an interviewer expects
**Difficulty:** Easy
**Python version:** Behaviour checked on CPython 3.11 (and in the page's Pyodide 3.11 runtime)

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words an interviewer expects. Every output block in the **Verified** section was copied from a real run of the examples on this pa

Question 10

What is the difference between a list and a tuple?

Accepted Answer

**Target Audience:** Beginners preparing for Python interviews — no prior Python knowledge assumed.
**Difficulty:** Easy
**Python version:** Behaviour checked on CPython 3.11 (python3.11 and the in-page Pyodide 0.25.1 runtime, which is CPython 3.11.3). Bytecode names are those of 3.11.

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact word an interviewer expects. Every output shown in the **Verified** se

PYTHONDECODED.

Easy

What is the difference between '==' and 'is'?

What are mutable and immutable types in Python?

How do you work with dictionaries (get, setdefault, items, merging)?

How does slicing with start:stop:step work?

What is the difference between append, extend and insert on a list?

How does iterable unpacking work?

How do you read TOML with tomllib in Python 3.11+?

Is Python pass-by-value or pass-by-reference?

Medium

What is the difference between shallow and deep copy?

How do uv workspaces and named dependency groups work?

What is the difference between an iterable and an iterator?

How does Pydantic v2 validation work (BaseModel, field_validator, mode)?

How does Polars LazyFrame query optimization work?

How does collections.deque work internally?

Why is using a mutable default argument dangerous?

What is composition versus inheritance?

Hard

What is an async iterator and async for?

How do TypeAdapter, strict mode, and computed fields work in Pydantic v2?

What is a weak reference in Python?

How does multiprocessing share data between processes?

What is the Method Resolution Order (MRO)?

What is TypeVarTuple and Unpack for variadic generics?

What is Python 3.12's free-threaded (no-GIL) build and what changes?